The proposed research program will develop a comprehensive understanding of the chemical structures, biosynthesis, and mechanism of the secondary metabolites used by the nematode Caenorhabditis elegans to control its development and physiology. We will focus on two important types of chemical signals: (1) The dauer pheromone, which C. elegans uses to induce development of the stress-resistant, dauer larval stage at high population densities. (2) A complex hybrid polyketide/ nonribosomal peptide (PK/NRP), which we have recently identified and shown is important for starvation-induced larval arrest. The dauer pheromone consists of several derivatives of the 3,6-dideoxy-L-sugar ascarylose, with different fatty acid-derived side chains. These ascarosides target G protein-coupled receptors in chemosensory neurons and downregulate the insulin and TGF? pathways, which regulate dauer formation, metabolism, and lifespan in C. elegans. In Aim 1 of this proposal, we will use a multi-disciplinary approach, including metabolomics, in vitro enzyme assays, organic synthesis of biosynthetic intermediates, and RNAi-based screens, to provide a general framework for ascaroside biosynthesis and its regulation. Our preliminary results, which show that secondary metabolism in C. elegans is closely tied to primary metabolism, have uncovered new, surprising roles for primary metabolic enzymes in ascaroside biosynthesis. We will investigate how different environmental conditions alter specific signaling pathways and downstream ascaroside biosynthetic enzymes, in order to modulate the chemical message that C. elegans communicates to the population. Thus, our work will establish when and how and why C. elegans produces different pheromones. At the fundamental level, these results will enable connections to be made regarding how animals respond to a changing environment and modulate their development and physiology, accordingly. In Aim 2 of this proposal, we will identify a complex hybrid PK/NRP produced by C. elegans. Although it has been noted that a few animals, including C. elegans, contain polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) genes, very little is known about these genes. Thus, we are breaking new ground in our work to characterize the structure, biosynthesis, and biological role of the PK/NRP. The domains in the C. elegans PKS/NRPS diverge significantly from those found in bacteria and fungi, and thus, by characterizing these domains, we will uncover unique enzymes and biosynthetic strategies. Our data suggest that the hybrid PK/NRP acts upstream of the insulin pathway and facilitates the metabolic changes that need to occur during starvation-induced larval arrest. The ascarosides and the PK/NRP are conserved chemical signals that are critical for the development and survival of many nematode species, including parasitic ones. Thus, our work will enable the development of chemical tools to interfere with the life cycles of parasitic nematodes and reduce their survival.